Norfolk County Mosquito Control Project

Mosquito Surveillance Program

The Norfolk County Mosquito Control Project uses several surveillance methods to measure mosquito populations across the county and to determine the dominate species. The data collected from these various surveillance methods assist the Project in making decisions as to what control measure, if any, should be employed. Post treatment surveillance is also used to judge efficacy of the various control methods.

Larval Mosquito Surveillance:

To determine the presence of mosquito larvae and their density personnel from the Norfolk County Mosquito Control Project use a surveillance tool called a dipper. dip3.jpg

Dipping, as this surveillance techniques is often referred to, is conducted before any larval control application is considered. This surveillance tool is used in advance of both the ground larval control program and the aerial helicopter larval control application. Larval surveys of rain basins are also conducted in advance of rain basin treatments using a device called a "Landers Ladle". 

Adult Mosquito Surveillance:

To determine the presence of adult mosquitoes and their density personnel from the Norfolk County Mosquito Control Project use light traps and landing counts.

Light Traps:

A New Jersey Light Trap is a device used for the sampling and identification of adult (flying) mosquitoes. This "trap" uses a 15 watt light bulb to attract the mosquito, and a fan draws the mosquito into a collection chamber. These traps are typically run once a week at sights located across the county. The collection chamber is then emptied and brought back to the lab for species identification. The New Jersey Light Traps are usually run throughout the mosquito season, typically from late May to some time in September or October. The trap sights have been placed in different habitats including salt marshes, inland marshes and upland areas so that a diversity of mosquito habitats can be sampled during the mosquito season. These light trap sites are set up in what are called "regional locations".

A CDC Miniature Light Trap CDC Light Trap is similar to a New Jersey Light Trap in that it also attracts adult mosquitoes using a light source. A fan then traps the mosquitoes in the collection chamber. The CDC Light Trap differs from a New Jersey Light Trap in that it is a portable light trap which runs off of batteries allowing field personnel to place these traps in remote areas. These traps have the added advantage of being moved quickly with minimal manpower. CDC Light Traps are often set out with CO2 canisters which release small amounts of CO2.  Traps baited with CO2 typically attract more human biting mosquito species. CDC Light Traps with CO2 are often used during EEE and West Nile Virus surveillance to collect mosquitoes for submission to the Massachusetts Arbovirus Surveillance Laboratory for the purpose of monitoring the presence of West Nile Virus and EEE in local mosquito populations.

Landing Counts:

Landing counts are performed by field staff who are directed to areas where human biting mosquitoes have been reported. The field employee then counts over a ten minute period how many mosquitoes land on them. Mosquitoes collected during this process are brought back to the lab for species identification. Landing counts are often conducted before (pre) and after (post) early morning aerosol applications to judge the efficacy of the application.

Gravid Mosquito Surveillance:

The Norfolk County Mosquito Control Project also uses a collection device called a Gravid Trap to sample mosquitoes. Gravid Trap

A gravid trap is a collection device which attracts "container breeding" mosquitoes. These are the mosquito species which lay their eggs in both natural and artificial containers. An example of a naturally occurring container would be a tree hole or rock pool. Examples of "man made or artificial" containers include tires, rain gutters, rain basins, old boats, kiddy pools and bird baths to name just a few. The gravid trap is composed of a tub which holds a rather aromatic brew of stagnant water mixed with hay or grass clippings. A collection box is mounted over the tub. When the mosquitoes are attracted to the stagnant water to lay their eggs the collection box fan sucks the mosquitoes into a collection chamber. These mosquitoes are then sorted by species and submitted to the Massachusetts Arbovirus Surveillance Laboratory for virus analysis. Gravid mosquitoes which are attracted to these traps are important to sample because they may have recently fed on a bird. The bird biting species are usually the first to pick up the virus since they feed primarily on birds where West Nile virus and EEE originate.